Anti-side-tone substation circuits



. I I Receiver? 1 I. I

3 F F19. E 8 I +4 P H. C. P YE I ANTISIDE TONE SUBSTATION CIRCUITS FiledMarch 3, 1926 /0 1' g3 m A? 9 J5 '2 1 L1 Y L H} RECEIVER I Imrantd'r"Harold C. F 5 WW Patented Get. 16, 1928.

UNITED A iiAnoLn c. PYE, or OAK PARK, ILLINOIS, ASSIGNOR TUAUTOMATICnnncrmo Inc, or CHICAGO, rumors, A conronarion or DELAWARE,

ANTI-summons snns'rarion erasures.

Application filfid Ma'fiill 3, 1926. Serial No 91,87'8.

This 'inventionrelates in general to telephone sub-station circuits, butmore especially to'sub station circuits for common battery telephonesystemsyand the principal object of the invention to provide a new andimproved common batteryanti side-tone telephone circuit.

in further object of this invention "is to provide a new and improvedtelephonesub station circuit in which are combined the ad'- vantages oi?the well known boostei type cir cuit and the common battery anti-sidetone circuit. y o

A further object of this invention is to provide an antiside-tone'sub-station circuit equipped with a calling device to permitits use on an automatic telephone system.

A'further object ofthis invention is to provide an anti side-tonebooster telephone circuit in which theamoimt of equipment requiredreduced to a minimum without impairing the efficiency of the sub-stationeither during the sending or the reception of the telephone signalsl :istill further object of this invention is to provide adirect currentreceiver con prising two windings which are'so proportioned as toperform the functions of a receiver and an induction'coilduringthefrecaption and transmission of signals by a telephonesub-station, and to also form the artificial line and balance necessaryto secure the anti side-tone effect duringthe transmission ofsignalsiit'rom the sub-station.

A still further object of this invention is to provide a sub-stationcircuit as above de'-' scribed adaptable for use-in a cradle typetelephone and using a three conductor cord to connect the handtelephoneto the desk stand.-

Further obj cots: not specifically mentionedhere,will be apparent fromthe detailed description and claims which follow.-

The drawings comprising Figs. 1, to 5, in-

elusive, show the' details of my invention. Fig. 1 shows the lllVGIltlOHadapted for use ina common battery manual telephone systom, thetransmitter and receiver being con- 'nected to the line equipment bymeans of the three cord conductors designated as C.

2, shows'the invention modified by the inclusion o'f'the callingdevicecomprising impulse springs 12 and shunt springs the transm tterand' receiver lll dlltllbil coil" again being connected to the line"equip I ment by the cord conductors designated as C. Fig. 3 shows thetelephone circuit as shown in with the modification in the ringerequipment that modification comprising a three plate condenser in placeof theordinary twoplate condenser shown elsewhere in the drawings. Theinclusion of this three plate condenser permits the detaching oilitheringer (i-t'ro'm the line conductor Qf'and attaching it to groundythereby adapting the sub-station for use in aground ringing system. i

Fig. 4: as a-schematicdiagram ofthe'suo station circuits during thetransmission of signals {from the sub-station.

Fig. 5 is a schematic drawing of the sub station circuit duringthereception of the signals by the sub-station Numerous anti side-tonesub-station telephone circuits have been devised prior to my 'inventonjthe various circuits obtaining the anti side-tone feature, by meansof an electrieal balance which reduces the two ends oi the receiver tothe same potential during the transmission ot signals from the sub-'oilt' signalsby the transmitter of the substation, the currentsgenerated thercinrwill divide themselves in the electrical net work 111a manner similar to the current division in xthe well known "lVheatstonebridge T The receiver whichoccupies disposition in the bridge circuitcorresponding to t-he gal vanometer,"isunresponsive "for the reason thatits"two'tcrmi'nals are reducedto the same potential. p V y t This systemotbalancing the electrical circuit of a telephonesubstation so thatthe:receiver terminals are brought to' xthe same potential duringtransmission of signals'from the substation, will {produce absolute Ianti J side tone effect only on' the line whose-circuit characteristics1 are identical -with the characteristics of the artificial line builtin the substatiom and then only on one par-i ticu-la'rl frequency.However; absolute *anti- -on the middle portion.

adding materially to the cost of production of the substation.

In order to reduce the cost of manufacture of the substation as much aspossible, I employ a direct current receiver, comprising two Windings,which are so proportioned that they may scrve as the wlndlngs of an:

induction coil, and so connected as to form the well known boostersubstation circuit. With an arrangeinent of this kind, I make no attemptto reduce the two terminals of the receiver to the same potential duringthe transmission of signals from the substation, rather I so proportionthe windings of the receiver induction coil so that during transmissionthe voltage generated in the transmitter, drives current through the receiver windings in opposite directions, those windings beingproportioned so that the current turn effect of these two currents isequal and opposite, and consequently no magnetism is set up in the coreof the receiver and the substation is consequently anti side-tone. Thesubstation built in the foregoing manner is very cheap to manufacture,

for the reason that it eliminates the costly permanent magnet receiver,the multiwinds ing induction coil and reduces the number of conductorsrequired between the trans nutter recelver unit and the line equipmentto a minimum.

Referring now to Fig. 1 in more detail,

across the incoming line conductors l and 2,

I have bridged the signalling equipment. comprising the condenser 5 andthe ringer- 6. Thisbridge is permanently closed, I have provided theordinary two circuit hook-- switch which comprises springslO and 11,which are opened when the substation is retired from use, to open thedirect current bridge across the line conductors 1 and 2, Thetransmitter 3 employed in'this circuit may be any well known commonbattery transmitter, and the receiver comprising the windings 7 and 8and the resistance 9 is of the direct current type, employing an E shapemagnetic iron core,;w1th the coils mounted InFig. 2, I have modifiedthesubstation circuit of Fig. 1, by the inclusion of the calling devicecomprlsing springs-12 and 13, 'and'furthermodified it by moving theresistance 9 from the receiver element, and attaching itto the condenser5 1n the same relative position in the circuit during the] transmissionand reception of telephone signals, but in such a position that it isnot shorted out by the shunt springs 13 during the impulsing period butrather is in the.

- spark quenching circuit provided for the imsistance comparablewith thecombined alue ofthe resistance of the coils 8 and arate resistanceelement is used.

Fig. 4;, shows the details of the talking circuit of any of the abovefigures, with arrows indicating the instantaneous direc tion of thealternating currents during the time that thesubstation is transmitting,that is, whenthe subscriber is talking into the transmitter 3. Thevarying transmitter resistance togetherwith the current flowing in theline circuit, produces an effectequivalent to setting up in thetransmitter a variable electromotive force which causes an alternatingcurrent to flow. This alternating current is superimposed upon thedirect cur rent flowing in the line circuit. The alter natingcurrent setup by the transmitter flows over a main circuit including the winding 8of the receiver, the resistance 9, the condenser 5, and the connectionsbetween those elements and the transmitter. The windings 7 and 8 of thereceiver form an auto transformer, with the winding 8 as the primary,thewinding 7 as the secondary; The alternating current flowing through theQif a sep-.

Winding 8 induces, in the winding 7, voltage which adds to thevoltageacross the terminals of the transmitter, so that the voltageimpressed upon the line terminals 1 and 2 is greater than that at theterminals of the transmitter, I thereby producing the -well knownbooster substation circuit. I The. current-turn ratios of the windings 7and 8 are'so chosen .that when combined with the resistance 9 and thecondenser 5, the current-turn strength of the winding 8 substantiallyneutralizes the current-turn strength ofthe winding'T, therebysubstantially preventing flux variations in the, core of the receiver 4.The core is magnetized by the direct current flowing through the winding7,. however, this magnetization is practicallyconstant and the diaphragmwill not be moved. side tone. V

Referring now to. Figure 5, which shows the sub-station-with arrowsindicating the current flow during the reception period, that is, whenthe source of potential is across the line conductors '1 and; 2,1 thecurrent The circuit is therefore anticoming in over the conductor 1,tends to divide in twopaths, the one including the transmitter 3 and thewinding 7, of the receiverto the line conductor 2, and the otherincluding the condenser 5, the resistance 9, and the windings 8and 7, ofthe receiver in series to the line conductor 2. The current flowingthrough the transmitter and winding 7 of the receiver, setsn in the coreof the receiver magnetism which induces in the winding'8, a backELMLF.which opposes the flow of alternating current in that winding, sothat'the portion of incoming current flowing over the last named parallel.

branch is extremely small. The flux set up by the current flowing in thewinding 7, acts upon the diaphragm of the receiver, to reproduce theincoming sound signal. Since the voltage induced in the winding 8, virtually prevents the flow of any alternating current through that vvinding,all of the energy received from the line conductors 1 and 2', except fora small part expended in the transmitter 3,is available to actuate thediaphragm of the receiver. By properly proportioning the windingT, withrespect to the transmitter 3, and thewinding 8 the resistance 9, andcondenser 5, I am able to construct a receiver whichwi-ll receive themaze imum possible amount of energy from the line circuit. v

This should be noted in both Figures 4 and 5, that the receiver windings7, 8, and

the resistance 9, are shunted by the ringer 6, which constitute acomplete circuitt'or both direct and alternating-currents. However, theringer is so constructed as to have a high resistance, and an evenhigher impedance, and therefore, the direct and alternating currentflowing through this ringer is so small as to be negligible in amountand effect, during the transmission and reception of signals by thesubstation.

Referringv now, particularlyto Fig. .2, it

will be noted, that I have removed resistance element9 from the receiver4, and connected it adjacent to the condenser 5. hen the calling devicecomprising springs 12 and 13, is operated, spring 13 operates first toclose a shunt circuit, which shunts out the trans mitter and receiver aslong as the calling device remains in an ofl'-normal position.Subsequent to the operation otsprings 13, the impulse springs 12arealternately opened and closed, to intermittently open the line circuitto transmit" impulses to the automatic switches at the central "station.When the springs 12 open the line circuit, they open the circuit of ahigh inductance relay in the exchange, with a resultant inductive kickwhich impresses a rather high voltage on the line conductors 1 and 2,unless,protective means are provided this high voltage will cause anarcing of the contacts 12, and will damage those contacts to thepoint-of uselessness.

As'is the custom in telephone sub-station circuits of this kind, I haveprovided a condenser 5 whlch is in a circuit so as to be bridged acrossthe contacts 12 when those contacts are open, the condenser absorbing acharge responsive to the hlgh voltremoving. the resistance 9 from thereceiver, 1

and attaching it as shown in Figure 2, I provide awl'iitl-ldlllg meanswhich is not short circuited, since the'circuittor the condenser age onthe line terminal. When the springs 12 again close their contacts,-thecondenser 5, closed by the contactspri'1'1gs-12, includes I theresistance 9 andthe ringerin' parallel,; shunt spring combination 13, totheone side of the spring 12, andhook switch 10 to the,

other side of the condenser. This resistance is ofsuch a value that' itretards the discharge of the condenser 5 sufficiently to protect thecontacts 12 of the fromserious damage.

A further advantage is gainedby placing the resistance 9 on thecondenser as shown calling device in Fig. 2. During impulsing theoperat-ing of shunt springs 13 place the resistance 9 directly acrossthe terminals ottheringer 6, thereby shunting the ringer to guardagainstits tapping when the impulse springs 12jopen the hue circuit and thecondenser 5 is being charged, as explained above. This arrangement makespossible the removal of the biasingspring with which ringers such as 6are usuallycquipped, I a a In Fig. 3, I have shown the circuit asl ig.

2, modified bythe inclusion of a 3 plate condenser, des gnated as 5 and5, the 5 portion of thecondenser being the ringing con-v denser andbeing so arranged as topermit:

the transfer of the connection of the ringer 6 from the lineconductorn2uto a ground connection-to permit grounded ringing, as is thecustom in some telephone systems. Three plate condensers, such as I haveshown here are formed by rolling three conducting plates together, witha suitable dielectric interposed between the plates, and with a suitableterminal attached to each plate. 'Such a condenser has the samecapacitance betwee'n'any two of its terminals. v

When a three plate condenser is used in connection with the circuitsabove referred to, the shunt around the ringer isinterrupted by thecondenser and ground connection of the ringer, WVhen the impulse springs12 interrupt] the line circuit, the condenser plate connected totheconductor 1 will be .charged to onepotential, and the plate connectedto the conductor 2 through the resistance 9 will be charged to an equaland opposite potential. The third condenser plate being interposedbetween the other two plates will be neutralized and will not receiveany charge, consequently the ringer, which is connected to this thirdplate, will receive no current and will not tap. V I

If desired the three plate condenser may be replaced by two condensers,which may be of difierent capacity it ringing conditions require. Inthis case, the ringer must be equipped with the usual biasing spring toprevent its tapping during impulsing.

There are many modifications in the details of the above circuits whichmay be made by one skilled in the art without de parting from the scopeof the invention. For example it may be advantageous to install acondenser such as 5 in the handtelephone, in the same relativecircuitposition as shown above; This will produce a hand telephone requiringonly atwo conductor cord, an instrument usable without a bellbox forextension phone installations. The hand telephone so constructed will befully anti side-tone incorporating all the principals hereinbefore setforth.

while said dial is being operated, said shunt springs also bridging saidimpulse springs .with said condenser and resistance-to eliminatesparking and connecting said resistance .in multiple with said ringer toprevent its tapping during impulsing.

2. In a substation set, a line circuit, a

transmitter, a ringer and: condenser, a re sistance,a;hook switch havinga plurality of normally open contactsets, a receiver having a pairofdifierentially wound windings, one of said windings 1n series with the lne circuit and the other in a shunt path around the transmitter, acalling device in said set having impulse springs'operated and shuntflsprings closed during the operation thereof, a circuit closed by saidshunt springs short circuiting both windings of said receiverandconnecting said resistance and alhook switch.

spring in a series multiple combination with said ringer, and anothercrcult closed by said shunt springs shunting one winding of said receiveraround said transmitter and shunting a secondhook switch contact set,

said condenser and resistance around said;

impulse springs, said condenser and hook [switch contact sets in theirnormal position preventing said shunt spring circuits from shortcircuiting said line circuit. 7

3. In telephone substation set, a receiver having two windings, a linecircuit, a transmitter, a calling device having impulse springs andshunt springs, a condenser and a ringer, resistance, said vcondenser andringer forming a permanent bridge across said line circuit, said impulsesprings, transmitter and one winding of said receiver forming a secondbridge across said line and said second winding and resistances forminga shunt path between the mid points of said first and second bridges toform an anti side tone booster substation, and means including saidshunt springs operated during the, operation of said calling device toshunt out said transmitter and receiver and to con- 'nect saidresistance in multiple with said ringer to prevent its tapping and tolower the impedance of-sa-id first bridge to prevent sparking at saidimpulse springs.

In witness whereof,; I'hereunto subscribe my name this'26th day ofFebruary,A. D.,

1926. a a w,

HAROLD C. PYE.

